I am struggling with the version of Blender for windows X64. I created a sphere inside a box (volume domain). The box was splitted in inlet, outlet, and so on ..... I found that there is no option to export in Engrid (*.bgec). Does anybody found the same problem? How can I work around?

If you used the installer for enGrid 1.4.0 or 1.4.x, then in the "start menu -> programs -> enGrid" you should see an option for "Browse Blender scripts" or something like that.
Then follow the add-on installation instructions provided at Blender's wiki, for installing each of the two scripts, one at a time: http://wiki.blender.org/index.php/Do...Python/Add-Ons

I already checked that the "Browse Blender scripts" is there. I opened with Notepad and I was able to see a bunch of the python scripts. Then I opened the blender and tried to follow the recommendations but i did not managed to find the tab "Add_on" on my Blender.

There is somethng wrong with the installation or there is a trick to see this Add_on tab?

I found that this problem is related with the version of blender. In 2.64a version I was able to find the Add_on tab and the script was installed. For 2.49b I was not able to find this tab...and i got no clue why. I will test the 2.49b and the i will post.

Since you're working on Windows and in Blender 2.49b: go into Blender's folder and create the sub-folder structure ".blender\scripts" and place the respective scripts inside that folder. It's the easiest way to install them on 2.49b.